This invention relates to a coal cutting machine carried by a gantry which is adapted to travel along the bed or frame of a longwall face conveyor. More particularly, the present invention relates to a coal mining machine having one or more coal cutting drums which project outwardly into the working face of the mine together with a roller crusher for subdividing lumps of coal while carried by a conveyor, wherein both the cutting drums and the roller crusher are supported for pivotal movement about horizontal axes.
In coal mining operations, the raw coal released by the cutting tools of a drum-type mining machine is loaded onto a conveyor partly by screw-shaped driving surfaces located at the periphery of the cutting drums and partly by guide plates located behind the cutting drums. However, as the mining machine moves along the longwall face of the mine, it has been discovered that portions of the longwall face of the mine frequently become detached and fall directly onto the conveyor. The detached and falling coal stems from cave-ins or "breakbacks" of the coal face and usually presents relatively large lumps of coal.
As a general rule, the mining machine with drum-type cutters travels along the face of the mine at a speed which is only a fraction of the operating speed of the longwall face conveyor. Typically, for example, an average speed for a mining machine is about 0.1 meter per second while a speed of about 0.3 meter per second is a quite common conveyor speed for a scraper chain-type conveyor. Thus, during times when the mining machine travels in either direction, and when it is stationary, there is an appreciable relative velocity between a gantry which supports the mining machine above a longwall face conveyor and the material transported by the conveyor. Now since the raw coal produced by cave-ins or breakbacks can reach the conveyor in the form of large lumps, it frequently occurs that these lumps are larger than the free space which exists between the conveyor and the gantry supporting the mining machine above the conveyor. These lumps of coal can and frequently do lead to blockages and other operating difficulties, particularly if they cannot pass through the portal opening of the gantry.
It is already known in the art to mount roller crushers on drum-type mining machines as, for example, in an associated relation with a support arm which carries one of the cutting drums of the mining machine. In this known arrangement, the roller crusher is actually mounted on the support arm at the side thereof opposite to the location of the cutting drum and parallel to the rotational axis thereof. The roller crusher is driven by the same drive system which rotates the cutting drum. This drive system is located within the support arm that carries both the cutting drum and the roller crusher.
It is another known arrangement to mount the shaft of a roller crusher directly in the frame of the mining machine and couple this shaft to the drive which rotates the cutting drum. In both of the above-known arrangements, the position or vertical height as well as the rotational speed of the roller crushers are fixed and cannot be matched to the actual operating conditions. It is impossible to independently position or rotatably control the roller crusher.